Send delayed emails through BuddyPress

I’m currently working on a website. And i wanted to create an (outside) messaging system in WordPress. The fact is we need to let the user send email to other domain. And we also need a delay system to send the mails, with a calendar for exemple !
We were looking for a solution on the web since 3 weeks, and we can’t manage to find anything. This is why we are looking for your help.